Device for regulating the average effect of an electric heating apparatus



1961 A. E. WlRMA 3,015,015

DEVICE FOR REGULATING THE AVERAGE EFFECT OF AN ELECTRIC HEATING APPARATUS Filed June 23. 1959 Fig. 1

xii q WM' Fig.3

' ire States The invention relates to an improved device for regulating the average effect of electric heating apparatuses, such as cooking plates, ovens, hot water heaters, fiat irons and the like. T he device is of a kind whichcperates to close and break alternately, at predetermined intervals, the circuit through the heating resistance of the apparatus to be controlled, and the relative average effect will then be determined by the proportion between the total length of the periods of current supply and the whole time of operation.

A known device of this type, to which the invention especially refers, uses a switch provided with a snap switch which closes and breaks the circuit in dependence on the curvature of a cooperating bimetallic member with a heating element of resistance wire, which is connected to either in parallel or series, the heating apparatus. Besides, manually operable means are provided for. adjusting the switch in such a way that a predetermined value on the average effect of the apparatus may be obtained. However, these known devices with a heating element of resistance wire generally make use of a plurality of movable parts, which results in complicated and expensive constructions liable to get damaged. These circumstances have to a considerable extent limited the use of energy regulators.

An object of the invention is to provide a durable energy regulator showing a high degree of accuracy. Another object is to provide a regulator which is simple and cheap and may be made in a small size, if desired.

According to the invention, a bimetallic member inserted in the circuit through the heating apparatus to be controlled has one end fixed to an adjustable support. Remote from this fixed end the member is formed with a contact surface adapted to cooperate with a snap switch also inserted in the circuit. Said bimetallic contact member is dimensioned and arranged, when the circuit is closed, to be heated by the current passing and thereby to bend on to said snap switch to cause it to snap into offposition. As the bimetallic contact member then returns due to its cooling, a resetting member on one of said contact members engages the other contact member to cause the snap switch to snap back from breaking into closing position. Further, means are provided for adjusting the support of the bimetallic member so as to place the contact surface of said member at a desired distance from the cooperating snap switch, whereby the length of the periods of current supply to the apparatus is determined.

In this device the current supplied to the heating apparatus will thus have to pass directly through the bimetallic member over the two cooperating contacts. Such a construction has been made possible by providing a bimetallic strip of a suflicient length and of a rather small cross section so that the resistance becomes suilicient to cause the required heating. According to a preferred embodiment the bimetallic strip may be V- or U-shaped, and its supported end may be mounted to another bimetallic strip designed and arranged to carry the first strip in such a way that the contact surface of the bimetallic contact member is kept in its intended position irrespective of changes in the temperature of the surrounding atmosphere.

'The invention will be described more in detailhereinatent @fihce Patented Dec. 26, l dl after with reference to the accompanying drawing in which FIGURE 1 is a section through a preferred embodiment of the regulating device showing the movable contact members in an initial or inoperative position,

FIGURE 2 shows the same section with said contact members in an operative position, and

FIGURE 3 shows diagrammatically a modified embodiment of the contact members.

In the drawing, a ,frame is formed by two spaced, parallel walls 4, one of which is shown in the figures, and an intermediate, rectangular block 5 of an insulating material, such as steatite, for instance. The walls 4 are firmly held onto two opposite end surfaces or the block '5 by means of tie rods 6 or similar connection members.

The block 5 has two holes to receive screws 7 and 8, the outer ends of which are threaded into terminals 9 and 10 respectively provided at the lower side of the block. Though not shown, the terminals are adapted to be connected in series to an electric circuit including a source of current and the heating apparatus to be controlled. Thus, one of the terminals 9, 10 may be connected directly to one end of said apparatus, while the other terminal is con- 'ectecl to one terminal of the source of current. Manually operable switches are preferably inserted in these connections, as is common in the art.

A conductor plate 11 supported by the upper side of the block 5 has one end clamped between the head of the screw 7 and an underlying portion of the block. The opposite end of the plate 11, which is bent a little upwards from the block surface, has fixed to it one end of a plate spring 12 extending rearwardly substantially in parallel to the plate 11. The spring 12 carries a contact head 13 on its free end. A tongue 14 extending from said head 13 is cut in the spring 12 and a flap 15 cut in the plate 11 is bent at right angles upwardly opposite to the end of the tongue 14. The tongue is compressed in its longitudinal direction to form an arc and its end engages a recess in the fiap 15. In this way the tongue imparts a pre-tension to the spring which will be bent a little in the same direction as the tongue, and when the spring is subjected to a force in straightening direction it can be caused to snap into an opposite position, as known from various snapcontacts.

A plate spring 16 having one end clamped between the head of the screw 8 and the block 5 is bent at right angles upwardly, and carries a compensation bimetallic member or strip 17 which is mounted at its base portion. A nut 18 is fixed to the upper leg of the plate spring 16 to receive a set screw 19 engaging the periphery of a cam 20 described hereinafter. The compensation mcmber 17 has its outer end connected to one end of a substantially U- shaped bimetallic member or strip 21. The free leg of the member 21 carries a contact head 22 just above the contact head 13, and the outer end of said free leg has fixed to it an angular member or plate 23 extending under the contact head 13. The plate 23 is made of an insulating material, such as steatite.

The U-shaped bimetallic member 21 is dimensioned to be heated by the electric current passing through it, when the contact heads 13 and 22 are in contact with each other. Of course, the dimensions of the strip 21 must be adapted to the heating effect but, as an example, it may be mentioned that within a range of 1200-1500 watt the strip 21 may have a width of 3-4 mm., a thickness of 0.3 mm. and a length of 45 cm. As known, bimetallic members are bent in dependence on the temperature, and in the embodiment shown, the bimetallic strip 21 is arranged in such a way that its end carrying the contact head 22 is lowered on heating and raised on cooling.

The compensation bimetallic member 17, on the other hand, has a cross section area suflicient to avoid any noticeable heating by the current passing. Said member 17 has for its purpose to compensate the influence of the temperature of the surrounding atmosphere. The arrangement is such that the free end of member 17 is raised on heating and lowered on cooling, is. quite contrary to the member 21, and thus it is possible to adapt the two bimetallic members 17 and 21 in such a way that the contact head 22 will be kept on the same level irrespective of the temperature of the surrounding atmosphere.

The cam 20 mentioned above is fixed to a shaft 24 which is journalled in the walls 4 of the frame. The shaft may be rotated by a knob, not shown, which is mounted on the shaft end projecting outside one of said walls. The shaft is preferably rotated in anti-clockwise direction in the figures, as indicated by arrows. in the initial or off-position shown in FIG. 1, the tip of the screw 19 rests on a cam portion having the smallest radius. As seen in clockwise direction, said cam portion is followed by a step 25, and from this step the radius increases continuously along about 270' up to a maximum radius at the point 26. The bimetallic member 17 is rather stiff, so that, when the set screw 19 slides along the cam periphery, the whole member 17 will be moved correspondingly in bending the supporting spring 16. Consequently, the contact head 22 will be raised and lowered in proportion to the radius of the cam portion engaging the screw 19, and in the initial position shown in FIG. 1 the contact head 22 is thus kept in its lowest position. This position may be adjusted by means of the set screw, if required.

The switches in the circuit outside the terminals 9, may suitably be operated by rotation of the shaft 24 in such a manner that they close before or at the same time as the screw 19 reaches the cam step 25, when the cam 21) is rotated anti-clockwise in FIG. 1. Hereby the apparatus may be operated exclusively by the knob fixed to the shaft 24. As the screw 19 rides upwards the cam step 25, the contact head 22 and the angular plate 23 are lifted correspondingly, whereby said plate 23 engages the lower side of the contact head 13 and forces it upwards. The snap switch 12 is thus caused to pass its unstable central position, whereupon it snaps into its opposite end position in which it is bent a little upwards. In this position the contact head 13 engages the contact head 22 with the result that the current passe through the circuit including the bimetallic member 21. Said member 21 will now be heated, whereby its free leg is lowered. Thus, the head 22 forces the head 13 downwards, and rather soon the spring will snap into its lower end position so that the circuit is broken. As the member 21 cools, it moves back upwardly, and at the same time the plate 23 engages the lower side of the head 13 and causes the spring 12 to snap into its upper position, where the head 13 contacts the head 22 so that the circuit is again closed. In this way the circuit will all the time be closed and broken alternately, and the relative length of the periods of closed and broken circuit will thus determine the average effect of the heating apparatus.

FIG. 2 shows an operative position in which the cam has been rotated about 30 in anti-clockwise direction, as compared with FIG. 1, so that the screw 19 has just been raised over the step 25. As seen, the spring 12 has here snapped into its upper end position in which the head 13 engages the head 22.

A further rotation of the cam 20 in the same direction brings about a further raising of the contact head 22. The result will be that, when the circuit has been broken as described, the bimetallic member 21 does not need to cool to the same extent as previously, before the plate 23 causes the contact 13 again to snap into closing position. In other words, the periods of heating become longer and the periods of cooling (broken circuit) correspondingly shorter, whereby the average efiect of the eating apparatus is increased. Preferably the cam 20 is which case the strip 21 can dimensioned such that the circuit will be closed practically all the time, when the screw 19 rests against the highest cam position 26.

The resetting member 23 must not necessarily be mounted on the bimetallic contact member but may instead be provided on the snap switch member 12. FIG. 3 shows diagrammatically such a modification. The function of this construction is the same as described above and therefore further explanations would be superfluous. Other modifications are, of course, also possible within the scope of the invention. Thus, the two bimetallic members may be designed in another way than described and possibly the member 17 may even be omitted, in be supported by the spring 16.

It may be noted that a device constructed according to the invention may be given considerably smaller size, as compared to the figures shown in the drawing, and thus the invention offers a reliable temperature regulator useful also for rather small heating apparatuses.

What 1 claim is:

l. A switching device comprising, a terminal plate, a plate spring having one end attached to said plate, said plate spring having a contact element at its opposite end, a lug on the terminal plate, an arched spring tongue for sed out of the plate spring and having an end engaging with the lug, a terminal having an upstanding springy bracket, a two-armed bimetallic member attached to said bracket, one of the arms thereof having an adjustable end portion, a shaft having a cam engaging said end portion to thereby adjust the position of the two-armed bimetallic member, the second arm of the bimetallic member being attached to one end of a second bimetallic member, the second end of the second bimetallic member carrying a contact adapted to either close or break circuit with the contact element on the plate spring, and a hook element of insulating material adapted, on elevating movement of the contact-bearing arm of the second bimetallic member to engage the plate spring and cause it to snap upwardly and bring its contact against the contact carried by the second bimetallic member.

2. A switching device as provided for in claim 1, wherein the hook element is secured to the end of the contact-carrying arm of the second bimetallic member.

3. A switching device as provided for in claim 1, wherein the hook element is carried by the plate spring.

4. A switching device comprising, a terminal, a spring plate secured thereto and having a contact at its end, a stressed spring tongue for normally maintaining the contact in switch-open position, a second terminal, a first bimetallic member attached thereto, a second bimetallic member secured to the first and having a contact member for co-operation with the contact member on the spring plate, a lifting member connected to one of the contactcarrying members and adapted to cause raising movement of the other contact-carrying member to thereby establish circuit-closure between the contacts when the first bimetallic member is moved to a predetermined position, and means for adjusting the position of the said first bimetallic member.

5. A device for regulating the average effect of an electric heating apparatus by alternately connecting and breaking the current in a circuit through the apparatus at predetermined intervals comprising, a bimetallic contact member connected in said circuit and having one end attached to an adjustable support, said bimetallic contact member having a contact surface at its free end, a snap switch contact member also connected in the circuit and adapted for cooperation with the contact surface on the bimetallic member to close and break the circuit, the bimetallic member being arranged, when the circuit is closed between it and the snap switch contact member, to be heated by the current passing through it and thereby to bend in such direction as to cause the snap switch contact member to snap into off position and away from the contact surface of the bimetallic member, a resetting member provided on the bimetallic contact members and arranged, when the bimetallic member assumes its nonheated position, to engage the snap switch contact memher to cause said snap switch contact member to be moved into circuit-closing position, and means for adjusting the support for the bimetallic contact member to position the contact surface of said member at a desired distance from the co-operating snap switch contact member, whereby the length of time of current supply to the apparatus will be determined.

6. A device for regulating the average effect of an electric heating apparatus by alternately connecting and breaking the current in a circuit through the apparatus at predetermined intervals comprising, a bimetallic contact member connected in said circuit, said contact member having a contact surface at its free end, a snap switch contact member also connected in the circuit and adapted for co-operation with the contact surface on the bimetallic contact member to close or break the circuit, the bimetallic contact member being arranged when the circuit is closed between it and the snap switch contact member, to be heated by the current passing through it and thereby to bend in such direction as to cause the snap switch contact member to snap into off position and away from the contact surface of the bimetallic contact member, the bimetallic contact member being carried by an adjustable second bimetallic member not subjected to heating by the electric current, said second bimetallic member being arranged to compensate the influence of the temperature of the surrounding atmosphere by bending in a direction opposite to the bending of the first bimetallic contact member, thereby maintaining the contact surface of the first bimetallic contact member in unchanged position.

7. A device according to claim 6, in which the second bimetallic member is provided with a set screw engaging the periphery of a rotatable cam disk.

References Cited in the file of this patent UNITED STATES PATENTS 2,135,864 Weber Nov. 8, 1938 2,498,127 Kuhn Feb. 21, 1950 2,673,269 Hobbs Mar. 23, 1954 

